gmrs antenna?

[jadmt]

curious will a magnetic antenna work on a square piece of aluminum work as a ground plane if a metal washer is glued to the aluminum? I have been running my antenna inside my jeep on the sport bar (buddy does the same) and it works great, but last week we tried something different traveling to Moab and we got right at 5 miles clear and at 6 miles was not so clear, which is no different and maybe a little worse than inside (two of us have the same exact set up and both agreed inside antenna might have been a little better)...this was on the interstate using mile markers..I started thinking maybe glueing a 10"X7" piece of aluminum on the roof would be even better...I only say a 10x7 piece is because that is what I have laying around...
will a bigger piece of aluminum with a washer work better than just the small metal square?

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[BDinTX]

I don't know the answer but have a question. Does the ground plane needs to actually be tied into the ground of the vehicle? Another thought, you could potentially put the aluminum on the inside of the roof and only put the antenna external.

 

[jadmt]

I don't know the answer but have a question. Does the ground plane needs to actually be tied into the ground of the vehicle? Another thought, you could potentially put the aluminum on the inside of the roof and only put the antenna external.

no...it was working with the little square piece of metal for 5 miles of clear talking (bottom photo)...not sure how I could put the antenna external if the aluminum was inside but even if I could I can't because I have a head liner on the inside...

 

[Mark75H]

On GMRS it will work fine.

 

[jadmt]

On GMRS it will work fine.

would you expect it to be better range with the first photo set up vs the second photo set up? I would use gorilla tape to tape the flat piece of aluminum to the top and then use gorilla tape to tape the steel washer to that....I didn't know if the tape would cause an issue as the washer would not actually be in contact with the aluminum..thanks..

 

[Mark75H]

I doubt you would notice any difference

 

[LazyJL]

A GMRS antenna works in the 460 MHZ frequency range and needs a ground plane with a minimum diameter of 13", 25" being preferable.
If the antenna you want to use is a "no ground plane" antenna, a metal ground plane may decrease its performance. Do you know type of antenna is it?
Being a magnetic mount, it's probable that it needs a ground plane.

 

[jadmt]

A GMRS antenna works in the 460 MHZ frequency range and needs a ground plane with a minimum diameter of 13", 25" being preferable.
If the antenna you want to use is a "no ground plane" antenna, a metal ground plane may decrease its performance. Do you know type of antenna is it?
Being a magnetic mount, it's probable that it needs a ground plane.

I have no idea but it is the antenna that comes with the midland mxt105. I will contact midland and ask.. thanks.

 

[Mark75H]

I suggest trying and seeing if you get the performance you need.

Antennas often confound theory.

 

[bd100]

Yes the aluminum plate probably will be an improvement.

I have the same antenna, but mount it on the back of the hood. Out of the way of tree branches, for one thing.

The simplest thing you can do is stick it onto one of the big hex bolts at the back of the hold, holding down the side cowl things where people attach ditch light brackets. Got pretty good performance from that alone.

It came with a little magnetic stick-on disc which I attached to the hood, near the back corner of the hood in front of the large trim with the windshield wipers. It's inline with the slot for the side cowl, placing the antenna near vertical. It is in sight of the driver but down low and very thin. I don't really notice it. Could have put it on the other side but that'd put it near the FM antenna. This puts the entire aluminum hood in front and to one side, and maybe 6" of hood to the left.

Three enhancements:

1) Ran a ground wire from the body to a hood bolt, to better ground the hood. Required figuring out the right nut to use to screw onto the bolt for the ring terminal, and another for the ground terminal on the body.

2) Also ran a ground wire from the hinge bolt under the hood backwards towards the windshield, in that slot at the edge of the side cowl. This forms a ground radial in the backwards direction.

3) Also cut the 20-foot long thin RG-174 cable to be just long enough to get under the hood, where I then put an inline connector to a thicker RG-58 cable which runs about 6 feet through the door weatherstrip and then under the steering wheel where the 275 is mounted. So the total length of cable is 1/3 as long, and has lower losses, for as long as that connector stays water tight under its layers of silicone sealing tape and electrical tape. But this part required buying a crimp tool, a crimp connector for RG-174, a connector for RG-58, and an adapter.

The end result is very good performance. And I can tuck it under the hood in case I'll be parking somewhere not so nice. Stopped worrying about that though.

But try just sticking it to the torx bolt at the back of the hood, for starters.

If you need a stick-on disc (may have to trim a side to match the contour of the hood):
https://theantennafarm.com/shop-by-...b/misc-antenna-parts/12656-taf-disc3-5-detail

If I were to do this again I'd probably get something like the following:

Magnetic NMO mounts with PL-259:
https://theantennafarm.com/shop-by-...etic-mounts/273-nmo-magnet-mounts-with-pl-259
Choose one with a 3.5" base and a shorter cable, if possible. And get the 3.5" stick-on plate mentioned above.

Your choice of GMRS mobile antenna. Select the NMO mount unless you want to skip the mount and go directly to a magnetic base antenna.
https://theantennafarm.com/shop-by-categories/antennas-mounts/mobile-antennas/gmrs-mobile-antennas

A quarter wave antenna will be around 6" tall, and better for mountains with people at different altitudes. I.e. talking with someone above or below you. And better for the forest with tree branches reaching out for the antenna. The taller antennas have some gain by squishing the signal towards the horizon, and would be better on the open flat lands. You could get one of each and switch as needed.

 

[Speed331]

My MTX275 set up

The 6db antenna mounted there perfectly matches the FM antenna on the other side. I have no problem hitting LOS repeaters out to about 40 miles - my swr is .05 to .07 through the whole gmrs band. The orientation of Jeep doesn't seem to matter at all - ie: having a ground plane or not. Radio checks come back 5x5 no matter which way I'm facing.
I carry the smaller 'ghost' antenna for days in the mountains where range is not as importaint as signal shape. Ie; dome vs flat.

 

[jadmt]

Yes the aluminum plate probably will be an improvement.

I have the same antenna, but mount it on the back of the hood. Out of the way of tree branches, for one thing.

The simplest thing you can do is stick it onto one of the big hex bolts at the back of the hold, holding down the side cowl things where people attach ditch light brackets. Got pretty good performance from that alone.

It came with a little magnetic stick-on disc which I attached to the hood, near the back corner of the hood in front of the large trim with the windshield wipers. It's inline with the slot for the side cowl, placing the antenna near vertical. It is in sight of the driver but down low and very thin. I don't really notice it. Could have put it on the other side but that'd put it near the FM antenna. This puts the entire aluminum hood in front and to one side, and maybe 6" of hood to the left.

Three enhancements:

1) Ran a ground wire from the body to a hood bolt, to better ground the hood. Required figuring out the right nut to use to screw onto the bolt for the ring terminal, and another for the ground terminal on the body.

2) Also ran a ground wire from the hinge bolt under the hood backwards towards the windshield, in that slot at the edge of the side cowl. This forms a ground radial in the backwards direction.

3) Also cut the 20-foot long thin RG-174 cable to be just long enough to get under the hood, where I then put an inline connector to a thicker RG-58 cable which runs about 6 feet through the door weatherstrip and then under the steering wheel where the 275 is mounted. So the total length of cable is 1/3 as long, and has lower losses, for as long as that connector stays water tight under its layers of silicone sealing tape and electrical tape. But this part required buying a crimp tool, a crimp connector for RG-174, a connector for RG-58, and an adapter.

The end result is very good performance. And I can tuck it under the hood in case I'll be parking somewhere not so nice. Stopped worrying about that though.

But try just sticking it to the torx bolt at the back of the hood, for starters.

If you need a stick-on disc (may have to trim a side to match the contour of the hood):
https://theantennafarm.com/shop-by-...b/misc-antenna-parts/12656-taf-disc3-5-detail

If I were to do this again I'd probably get something like the following:

Magnetic NMO mounts with PL-259:
https://theantennafarm.com/shop-by-...etic-mounts/273-nmo-magnet-mounts-with-pl-259
Choose one with a 3.5" base and a shorter cable, if possible. And get the 3.5" stick-on plate mentioned above.

Your choice of GMRS mobile antenna. Select the NMO mount unless you want to skip the mount and go directly to a magnetic base antenna.
https://theantennafarm.com/shop-by-categories/antennas-mounts/mobile-antennas/gmrs-mobile-antennas

A quarter wave antenna will be around 6" tall, and better for mountains with people at different altitudes. I.e. talking with someone above or below you. And better for the forest with tree branches reaching out for the antenna. The taller antennas have some gain by squishing the signal towards the horizon, and would be better on the open flat lands. You could get one of each and switch as needed.

$30 for a stick on metal disc? I wonder what makes it worth that much. Your set is great but I want simple as I only use the radio when off-roading. I want to keep antenna in the back as well.

what is the difference I wonder in the more expensive NMO magnetic mount vs the cheaper ones?

 

[jadmt]

A GMRS antenna works in the 460 MHZ frequency range and needs a ground plane with a minimum diameter of 13", 25" being preferable.
If the antenna you want to use is a "no ground plane" antenna, a metal ground plane may decrease its performance. Do you know type of antenna is it?
Being a magnetic mount, it's probable that it needs a ground plane.

Midland is quick to respond they said they recommend a 4 to 6 inch diameter ground plane.

 

[djthumper]

You minimum size ground plane for GMRS is about 6". On a friend's Jeep we used a piece of thin steel and painted the top surface, we sanded the mating surface and used contact cement to the roof panel.

 

[USNvet]

According to "The Swiss Guy" ground planes can be as simple as adding a little copper wire to the base of your antenna, plus making sure the impedance matches everywhere. No flat chunk of metal needed. Add a cheap VNA to supertune the antenna and ground plane. If you find the below video helpful, his video #188 probably covers how to DIY stuff! (Turns out video #188 is just tech and spec blah blah blah, but #368 does show creation of a simple ground plane antenna)

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